Brother asking share in Self acquired property

You can not stop anyone proceeding against you, and you can only defend that litigation in such court.  Borrowing money from members of a family while constructing house is not strange or new, and that borrowing may not give ownership title to mother or someone to claim a share.  Do not be disturbed by such threats, and as you are in possession since 2000, the chances of filing a suit are very remote.  Before filing a suit, there si a process of replying to a notice from your brother, and entrust this reply to an expert advocate for deft drafting.

If the property is in your name by sale then forget whatever he says. He cannot do anything just tell him to go to court of law. 

You have the absolute discretion to ignore his demand.